By using an electro-slag re-melting procedure, new shielding steel alloys with varying chromium concentrations ranging from 2 to 18%, and a reduced nickel content of roughly 12% were developed. The ...mass attenuation μm, mean free path (MFP), effective atomic number Zeff, and electron density Neff, the energy buildup factor (EBF), and the energy absorption buildup factor (EABF) were calculated for the new developed steel alloys by using Phy-X/PSD software over the photon energy range (0,015–15 MeV). Furthermore, using the NGCAL online software, the macroscopic effective neutron removal cross-sections (ΣR) for 25.4 meV thermal neutrons, 4 MeV fast neutrons, and 10 MeV fast neutrons were determined. All cobalt-free steel prepared samples (S1, S2, S3, S4, and S5) were found to have lower mean free path (MFP) and half-value layer (HVL) values, as well as greater macroscopic effective neutrons removal cross section (ΣR) values, than their estimated equivalents for both carbon steel and stainless steel. Furthermore, based on the estimated values for the mean free path (MFP), the half-value layer (HVL), and the effective neutrons removal cross section (R), sample S5 with the greatest chromium content (17.68%) is shown to be a good candidate for gamma shielding rather than neutron shielding.
•A new developed steel alloys were developed to serve as a shielding material in the nuclear industry & applications.•Gamma shielding parameters were calculated.•Neutron removal cross section was calculated.•The developed samples have importance in the nuclear applications.
Fluency is an essential component in writing ability and development. Writing fluency research is important to researchers and teachers interested in facilitating students' written text production ...and in assessing writing. This calls for reaching a better understanding of writing fluency and how it should be measured. Although fluency is the construct with the most varied definitions and measures in writing research, such large variance in conceptualizing the construct is rarely discussed. In an attempt to demystify the what of this construct, the present article reviews its definitions, shows how its measurement has been influenced by oral production research, and discusses some issues related to the validity of the varied measures used for assessing it.
The ability of metal-free gas to cool by molecular hydrogen in primordial haloes is strongly associated with the strength of ultraviolet (UV) flux produced by the stellar populations in the first ...galaxies. Depending on the stellar spectrum, these UV photons can either dissociate H2 molecules directly or indirectly by photodetachment of H− as the latter provides the main pathway for H2 formation in the early universe. In this study, we aim to determine the critical strength of the UV flux above which the formation of molecular hydrogen remains suppressed for a sample of five distinct haloes at z > 10 by employing a higher order chemical solver and a Jeans resolution of 32 cells. We presume that such flux is emitted by Pop II stars implying atmospheric temperatures of 104 K. We performed three-dimensional cosmological simulations and varied the strength of the UV flux below the Lyman limit in units of J
21. Our findings show that the value of
$J_{21}^{\rm crit}$
varies from halo to halo and is sensitive to the local thermal conditions of the gas. For the simulated haloes, it varies from 400 to 700 with the exception of one halo where
$J_{21}^{\rm crit} \ge 1500$
. This has important implications for the formation of direct collapse black holes and their estimated population at z > 6. It reduces the number density of direct collapse black holes by almost three orders of magnitude compared to the previous estimates.
(a) JJAS rainfall climatology (mm month−1) for the years 1951–2005 using CRU (1951–2005) data set. The rectangular box (5°–35°N and 70°–100°E) represents the Indo‐Pakistan summer monsoon region. (b) ...JJAS rainfall trends (mm month−1 year−1, shades) using CRU data set. Five percent significant values are shown by dots. (c) JJAS climatology of VIMMT (kg m−1 s−1 month−1) for the period 1951–2005. (d) Same as (c) except for trends (kg m−1 s−1 year−1, shades) of VIMMT. Five percent significant values are shown by dots and are omitted where the slopes of moisture transport range between 0.2 and −0.2 (kg m−1 s−1 year). In (d), the contour interval is 0.1 except the initial (±0.05, shaded as white colour).
ABSTRACT
Understanding the effects of climate change and global warming on the South Asian summer monsoon rainfall trend is critically important for millions of inhabitants of this region. This study investigates seasonal (June–September) rainfall trend over the Indo‐Pakistan subcontinent by using 36 climate model outputs from the World Climate Research Programme's Coupled Model Inter‐comparison Project Phase 5. The historical (1951–2005) and future (2006–2100) simulations under two representative concentration pathways (RCPs), RCP4.5 and RCP8.5, are analysed for this purpose. Model reproducibility is evaluated based on spatial correlation of seasonal rainfall and vertically integrated meridional moisture transport between simulated and observed fields. It is found that the majority of models shows reasonable skill in capturing the observed pattern of rainfall climatology and trend over the subcontinent. Our results showed that the models are more skilful in simulating seasonal mean moisture transport than trend over the Arabian Sea and Bay of Bengal. Of the 36 models analysed, only two models HadGEM2‐AO and CNRM‐CM5 closely approximate both the climatology and trend based on statistical performance metrics. Our results suggest that the strengthening of northwards moisture transport over the Arabian Sea and Bay of Bengal is a likely reason for the increasing rainfall trend over Indo‐Pakistan subcontinent in a warmer climate. The RCP8.5 indicates marked increase in both rainfall and moisture transport trends compared to RCP4.5 forcing scenario.
This study assessed the restorative dietary effects of Moringa oleifera (MO) leaves extract against the negative impacts of sub-lethal fipronil (FIP) toxicity in Nile tilapia. To achieve this ...purpose, the growth, body composition, haemato-biochemical measurements, serum immunity, and antioxidant condition of Nile tilapia have been examined. Fish were arranged into 6 experimental groups in quadruplicates. Three groups were fed on diets supplemented with 0.0 (reference group), 1.0 (MO1), and 2.0 (MO2) g kg
of MO leaf extract. The other three groups were fed on the same MO levels and concomitantly subjected to a sub-lethal FIP concentration (4.2 µg L
for 3 h only per day) and defined as FIP, FIP + MO1, and FIP + MO2. The experiment lasted for 8 weeks. Results unveiled that growth parameters were significantly decreased alongside an increased feed conversion ratio in the FIP-intoxicated group. The moisture and crude protein (%) were decreased significantly together with a significant increase of the crude lipids (%) in the fish body of the FIP group. Sub-lethal FIP toxicity induced hypochromic anemia, leukopenia, hypoproteinemia, hypoalbuminemia, hypoglobulinemia, and hepato-renal failure (increased urea and creatinine concentrations, as well as ALT and AST enzymes). Exposure to sub-lethal FIP also induced (a) immunosuppression manifested by a decline in total IgM, complement C3, and lysozyme activities, (b) enzymatic antioxidant misbalance manifested by decreases in SOD and CAT activities, and (c) oxidative stress (declined T-AOC and elevated of MDA concentrations). On the other side, dietary supplementation with MO leaf extract in FIP + MO1 and FIP + MO2 groups noticeably modulated the aforementioned parameters. Therefore, we can conclude that dietary MO could reduce sub-lethal FIP toxicity in Nile tilapia with a possible recommendation for regular prophylaxis supplementation in Nile tilapia diets.
Massive primordial halos exposed to moderate UV backgrounds are the potential birthplaces of supermassive black holes. In these halos, an initially isothermal collapse will occur, leading to high ...accretion rates of ~0.1 M⊙ yr-1. During the collapse, the gas in the interior will turn into a molecular state, and will form accretion disk in order to conserve angular momentum. We consider here the structure of such an accretion disk and the role of viscous heating in the presence of high accretion rates for a central star of 10, 100, and 104 M⊙. Our results show that the temperature in the disk increases considerably due to viscous heating, leading to a transition from the molecular to the atomic cooling phase. We found that the atomic cooling regime may extend out to several 100 AU for a 104 M⊙ central star and that it provides substantial support to stabilize the disk. It therefore favors the formation of a massive central object. The comparison of clump migration and contraction time scales shows that stellar feedback from these clumps may occur during the later stages of the evolution. Overall, viscous heating provides an important pathway to obtain an atomic gas phase within the center of the halo, and helps in the formation of very massive objects. The massive object may collapse to form a massive black hole of about ≥104 M⊙.
Abstract
Oxidative desulfurization (ODS) is considered to be one of the most promising desulfurization processes as it is energy-efficient and requires mild operating conditions. In this study, a ...novel green synthesized Al- based metal–organic framework with high surface area has been synthesized hydrothermally using waste polyethylene terephthalate bottles (PET) as a source of terephthalic acid as an organic linker. The prepared Al based MOF have been characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM). The catalytic activity of the prepared Al-MOF was evaluated in the oxidative desulfurization (ODS) of both modeled and real crude oil samples. The different operating parameters (temperature, time, catalyst dose, oxidant loading and sonication) on the ODS performance have been optimized. The optimal conditions for maximum removal of thiophene from modeled oil samples were found to be 30 min, 0.5 g of catalyst and 1:3 oil to oxidant ratio. Under the optimized conditions, sulfur removal in real oil samples obtained from Alexandria petroleum company was 90%. The results revealed that, the presented approach is credited to cost-effectiveness, environmental benignity, and ease of preparation, predicting great prospects for desulfurization of fuel oils on a commercial level.
Twentieth century climate exhibits a strong warming trend. There is a broad scientific consensus that the warming contains a significant contribution from enhanced atmospheric greenhouse gas (GHG) ...concentrations due to anthropogenic emissions. The climate will continue to warm during the 21st century due to the large inertia of the Earth System and in response to additional GHG emissions, but by how much remains highly uncertain. This is mainly due to three factors: natural variability, model uncertainty, and GHG emission scenario uncertainty. Uncertainty due to natural variability dominates at short time scales of a few years up to a few decades, while at the longer centennial time scales scenario uncertainty provides the largest contribution to the total uncertainty. Model uncertainty is important at all lead times. Furthermore, our understanding of the Earth System dynamics is incomplete. Potentially important feedbacks such as the carbon cycle feedback are not well understood and not even taken into account in many model projections. Yet the scientific evidence is overwhelming that the global mean surface temperature will exceed a level toward the end of the 21st century that will be unprecedented during the history of mankind, even if strong measures are taken to reduce global GHG emissions. It is this long-term perspective that demands immediate political action.
►Climate projections for the 21st century are inherently uncertain. ►The uncertainty in the climate projections can be potentially reduced. ►Some feedbacks determining the rate of global warming are not well understood. ►The Earth will warm to a level unprecedented in man's history.
Vast amounts of methane hydrates are potentially stored in sediments along the continental margins, owing their stability to low temperature – high pressure conditions. Global warming could ...destabilize these hydrates and cause a release of methane (CH4) into the water column and possibly the atmosphere. Since the Arctic has and will be warmed considerably, Arctic bottom water temperatures and their future evolution projected by a climate model were analyzed. The resulting warming is spatially inhomogeneous, with the strongest impact on shallow regions affected by Atlantic inflow. Within the next 100 years, the warming affects 25% of shallow and mid‐depth regions containing methane hydrates. Release of methane from melting hydrates in these areas could enhance ocean acidification and oxygen depletion in the water column. The impact of methane release on global warming, however, would not be significant within the considered time span.
Key Points
Arctic bottom water temperatures will rise under climate warming
Methane hydrates will be released in the coming decades
The release will be limited in the next decades and lead to ocean acidification
In this paper, using Lie point symmetry analysis, we study the dynamics of the solitons for the nonlinear Schrodinger’s equation with anti-cubic nonlinearity. Some new doubly periodic solutions are ...obtained that degenerate to dark and bright soliton solutions. In our of best knowledge, the obtained solutions are new. Those obtained results have important applications in the understanding the nonlinear propagation theory of solitons in metamaterials.
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